Investigation of the Mature of the y Rays. 
667 
of symmetry arises. On the pulse theory the particles should 
go equally backwards and forwards; indeed, if they were 
ejected by atomic explosions, the result of energy accumu- 
lated by passing pulses as suggested by J. J. Thomson in 
the case of X rays, they would move equally in all 
directions.] 
Wigger gives a table (Jakrbuch der Radioaktivitdt, Bd. ii. 
p. 431) showing that the y rays are absorbed according to a 
density law pretty strictly, except for the smaller thicknesses 
in the case of the substances of larger atomic weight. 
Assume this law to hold good : and also assume for the 
present that the absorption of /3 rays follows the density 
law. The latter is only roughly true, of course ; but we 
may deal with quantities in a broad fashion first, and make 
the proper amendments afterwards. 
We can now compare the quantities of cathode radiation 
Fig. 4. 
A fhC 2> 
->; 
/-/ 
A'C' # 
f 
;>-/ 
which should emerge from the far sides of two plates of 
different densities, p and p' '. Let these be represented by 
AD and A'D' in the figure ; and let BC and B'C be cor- 
responding strata of equal weight, in fact let AB/A 7 B' = 
BC/B'C^CD/C'D^p'/p. Let the plates be crossed by 
equal pencils of y rays, as shown in the figure. A certain 
quantity of y radiation is absorbed in crossing BC : in the 
language of our present hypothesis we should say that a 
certain number of y particles are stripped of their positives, 
and the negative remainders go cm. An equal number of 
